Treatment of vascular lesion using a catheter is widely performed because it introduces less surgical stress in a living body. For example, a balloon catheter is used for dilating a lesion area in a coronary artery and improving a blood flow in Percutaneous Transluminal Coronary Angioplasty (PTCA). The balloon catheter generally includes an elongated hollow catheter shaft, a balloon provided on a distal side of the catheter shaft, and a hub provided on a proximal side of the catheter shaft.
The catheter shaft is required to have a pushing performance which contributes to reliably transmit a pushing force of an operator from a proximal side to a distal side of the catheter because the catheter may be inserted into blood vessels having complicated curves. The catheter shaft also needs to have a followability (i.e., maneuverability) which helps to smoothly and reliably advance the catheter in a blood vessel in a living body along a leading guide wire. Catheters are known to be configured to achieve both of these properties by making a proximal side of a catheter shaft of a material having a high flexural stiffness and a distal side of the catheter shaft of a material having less flexural stiffness than the proximal side and being relatively highly flexible (i.e., possess relatively high flexibility), and joining both sides together in an axial direction. For example, Japanese Patent Application No. 2013-005976 discloses a catheter with a catheter shaft having a high flexural stiffness joined to a distal catheter shaft having less flexural stiffness.